Few questions about grounding and bonding

[Electricalartist]

Hey im new to this forum . Im studying grounding and bonding from both the Mike holt dvd and book and the soares book. I CAN NOT GRASP THE DIFFERENCE. From what I'm understanding is the neutral wire gets a connection to the earth 1 time only. That i understand

What I can not get is the difference between system grounding, equipment grounding, and bonding. It seems like equipment grounding is actually bonding and is the green wire we use to connect our equipment and metal enclosures a ground or bond?

 

[Electricalartist]

If you look at these 2 pictures from the soares book one shows the motor to be grounded and the other shows the motor to be bonded. The green wire is shown as a ground , the ground bar is shown as a bond ,the pipe in between the panels one shows it as a ground the other says it's bonded

 

[augie47]

Often the difference is a "fine line". Bonding equipment simply means the equipment is connected together so that the components are at virtually the same potential (for instance, we bond swimming pool equipment). Equipment grounding connects the equipment to the grounded conductor or grounding electrode at the service by use of an equipment grounding conductor. Once a piece of equipment is grounded, the equipment bonded to it will be grounded also.

 

[Electricalartist]

Often the difference is a "fine line". Bonding equipment simply means the equipment is connected together so that the components are at virtually the same potential (for instance, we bond swimming pool equipment). Equipment grounding connects the equipment to the grounded conductor or grounding electrode at the service by use of an equipment grounding conductor. Once a piece of equipment is grounded, the equipment bonded to it will be grounded also.

So if I run a romex wire to a switch with a metal box, I take the bare wire and connect it to the box and then to the green screw on the switch. Is this box bonded or grounded, is the switch bonded or grounded

 

[roger]

So if I run a romex wire to a switch with a metal box, I take the bare wire and connect it to the box and then to the green screw on the switch. Is this box bonded or grounded, is the switch bonded or grounded

It is bonded and per the NEC language it is also grounded. Unfortunately these two words can mean the same thing.

Roger

 

[Electricalartist]

Im reading these books and it's really hard to understand what I'm reading if things are not a bit clearer. What is system grounding, is it only taking the nuetral and bringing it to a grounding electrode?

 

[user 100]

So if I run a romex wire to a switch with a metal box, I take the bare wire and connect it to the box and then to the green screw on the switch. Is this box bonded or grounded, is the switch bonded or grounded

The non current carrying metal parts of the sw and box would be bonded....

Think of bonding as in "connecting together" or bonded as "connected to"...-

The bonded equipment is grounded because it is ultimately connected to the grounded conductor (neutral) at your panel, as there must be a low impedance path back to the source for fault current to ensure rapid opening of an ocpd in the event of a ground fault (hot wire hitting bonded case of equipment).

 

[Electricalartist]

The non current carrying metal parts of the sw and box would be bonded....

Think of bonding as in "connecting together" or bonded as "connected to"...-

The bonded equipment is grounded because it is ultimately connected to the grounded conductor (neutral) at your panel, as there must be a low impedance path back to the source for fault current to ensure rapid opening of an ocpd in the event of a ground fault (hot wire hitting bonded case of equipment).

With the switch bonded and grounded, a hot wire hits the box, now this current going thru the box goes back to source and not the earth?

If the box gets hit by lightning, the lightning will go to earth and probably most likely also the circuit source?

 

[augie47]

Im reading these books and it's really hard to understand what I'm reading if things are not a bit clearer. What is system grounding, is it only taking the neutral and bringing it to a grounding electrode?

The simplest answer would be "correct" and it's likely that's what you will always see, but, on a bit more complicated plane, there are systems that have no neutrals where one of the phases can be grounded.

 

[user 100]

With the switch bonded and grounded, a hot wire hits the box, now this current going thru the box goes back to source and not the earth?

Yes- current is always trying to return to its source, not the earth. Even though earth can be one of many potential paths, it is a poor one because it is so high in impendance.

The lower a paths impedance back to the source, the higher the amount of current that path will carry. If you have a svc neutral with 0.5 ohm of resistance, and a 120 volt fault (that hot wire hitting that bonded box) in a correctly bonded/grounded system, your total fault current will be 240 amps- the 15 or 20 amp breaker will open instantly de-energizing the box/ exposed metal parts.

A ground rod on the other hand that has 15 ohms resistance (thats being generous as many have values far exceeding that...) would only allow 8 amps of fault current....

If the box gets hit by lightning, the lightning will go to earth and probably most likely also the circuit source?

With lightning all bets are off- it will go where it wants to go- a rod might help shunt some of the energy to the the earth. A rod may be benefical if there is a primary that drops on a secondary, otherwise it has no real benefit.

 

[Electricalartist]

I think I understand better now. The system grounding is the grounding electrode connection to neutral to bleed overvoltage from lighting
The equipment bonding is continuity on metal parts of equipment so if the metal gets a fault the breaker will trip
Equipment grounding is sometimes a combination of grounding a bonding and is for lightning purpose ?

 

[GoldDigger]

It is bonded and per the NEC language it is also grounded. Unfortunately these two words can mean the same thing.

Roger

I have a quibble with that statement. The definitions of the two words are fixed and always apply when trying to determine meaning. I think what you are saying is that they can (often) refer to or apply to the same thing. They never mean the same thing.

For example, we would never say that "light colored" and "pink" mean the same thing, although they may both describe a particular colored object.

 

[roger]

I think what you are saying is that they can (often) refer to or apply to the same thing. They never mean the same thing.

You're preaching the choir here. The problem is the NEC wording that crosses over when applying the words bonding and grounding, Don has tried for years to get it changed in ROP's but the CMP(s) will not change it. It would be much easier for people new to the trade to understand if the term EGC was simply EBC.

Roger

 

[GoldDigger]

You're preaching the choir here. The problem is the NEC wording that crosses over when applying the words bonding and grounding, Don has tried for years to get it changed in ROP's but the CMP(s) will not change it. It would be much easier for people new to the trade to understand if the term EGC was simply EBC.

Roger

I agree completely with that sentiment.

 

[Electricalartist]

Ok so is it safe to say that equipment grounding is sometimes also equipment bonding. In the case of a lighting strike the high lightning voltage goes to earth and in the case of a fault the fault current goes back to its source? So the egc acts as both a bond and ground and this is where the confusion is?

 

[dionysius]

I have been where the OP is at.

Whatever way you cut it bonding and grounding are intersecting sets, no disjoint sets.

Bring on your definitions and I will be able to show you that what I stated is true.

This is a problem as old as the use of language and the need for disambiguation.

 

[electrofelon]

Most of the confusion comes from the fact that your typical EGC is serving multiple purposes: its providing a low impedance path back to source, connecting the equipment to earth, and bonding everything together. I think it would cause less confusion to call it an "equipment bonding conductor" instead of "equipment grounding conductor."

I think in my perfect world, system grounding would be pulled out into its own article, say 249, since it has nothing to do with equipment earthing and fault clearing. Then Article 250 would be called bonding, and equipment earthing and equipment bonding would be subcategories of that. There would be a statement in 250 saying that a single conductor can serve as both the equipment earthing and equipment bonding conductor. Not really sure where to stick the grounding electrode system. Probably that could get it own article, call it 248, which would further help separate earthing from fault clearing to help fight the myth. Then 249 and 250 would reference 248 as needed.

 

[Smart $]

Ok so is it safe to say that equipment grounding is sometimes also equipment bonding. In the case of a lighting strike the high lightning voltage goes to earth and in the case of a fault the fault current goes back to its source? So the egc acts as both a bond and ground and this is where the confusion is?

When in doubt, the definitions will always apply (in general).

Bonded (Bonding). Connected to establish electrical continuity
and conductivity.

Bonding Conductor or Jumper. A reliable conductor to
ensure the required electrical conductivity between metal
parts required to be electrically connected.

Bonding Jumper, Equipment. The connection between two
or more portions of the equipment grounding conductor.

Bonding Jumper, Main. The connection between the
grounded circuit conductor and the equipment grounding
conductor at the service.

Bonding Jumper, System. The connection between the
grounded circuit conductor and the supply-side bonding
jumper, or the equipment grounding conductor, or both, at a
separately derived system.

Ground. The earth.

Ground Fault. An unintentional, electrically conductive
connection between an ungrounded conductor of an electrical
circuit and the normally non–current-carrying conductors,
metallic enclosures, metallic raceways, metallic equipment,
or earth.

Grounded (Grounding). Connected (connecting) to
ground or to a conductive body that extends the ground
connection.

Grounded, Solidly. Connected to ground without inserting
any resistor or impedance device.

Grounded Conductor. A system or circuit conductor that
is intentionally grounded.


Grounding Conductor, Equipment (EGC). The conductive
path(s) that provides a ground-fault current path and connects
normally non–current-carrying metal parts of equipment
together and to the system grounded conductor or to the
grounding electrode conductor, or both.

Informational Note No. 1: It is recognized that the equipment​

grounding conductor also performs bonding.​

Informational Note No. 2: See 250.118 for a list of acceptable​

equipment grounding conductors.​

Grounding Electrode. A conducting object through which
a direct connection to earth is established.

Grounding Electrode Conductor. A conductor used to
connect the system grounded conductor or the equipment to
a grounding electrode or to a point on the grounding electrode
system.

As to the finer understanding of the difference between an EGC and an EBJ is that EGC's are required to be and only run with the circuit conductors. EBJ's are not required to be run with circuit conductors but may be required to bond metal parts serving as an EGC together.

 

[Smart $]

.... EBJ's are not required to be run with circuit conductors but may be required to bond metal parts serving as an EGC together.

An example of an EBJ is the required jumper around an expansion joint installed in a metal raceway.

 

[dionysius]

Thank you for the definitions, Smart$.

Going through them carefully confirm and support my generalized statement above:

"Bonding and Grounding are intersecting sets, not disjoint sets"

​

Since we are here to learn, not to prove ourselves infallible, I welcome challengers to the statement. The code books should use that generalization since it would remove confusion for new readers such as OP.